"Rain is likely to pick up late Tuesday afternoon into the evening and push through until Wednesday morning.

"Tuesday is the day of greatest concern for us at the moment."

Up to 200mm more rain could fall in parts of the Northern Rivers district over the following two days and some catchments may receive higher, the bureau said late Monday afternoon.

However motorists returning from long-weekend getaways were being urged to take extra caution, especially if travelling in the north and mid north coastal regions, with high tides and rain expected on Monday evening, Ms Gollings said.